Originally posted by timbo For large rooms, is it best to use little slave flashes to avoid harsh shadowing?
It really dpends on the type of illumination in the room, the type of activity taking place, whether you will move around, etc.
Originally posted by timbo Where is best to position slaves in these situations?
I'd say if you want to preserve the mood, either bounce the flash (flashes) to the ceiling, use two flashes facing each other (above the heads, pointing down) to both sides of you, or use a camera-mounted flash with a good diffuser such as a portable softbox or stofen/lightsphere mod.
Originally posted by timbo behind the subjects, but hidden from direct camera view?
That would create cool effects but create silhouettes.
Originally posted by timbo I'd like to keep an element of atmosphere if possible, which I've only been able to achieve so far without a flash.
I understand. One thing I've seen done effectively is to mount a flash on the camera, zoom the head quite a bit and directly illuminate one single person, isolating that person from the group. In particular, it works well with dancers and parties.
Originally posted by timbo Macro:
I need something that can be used in pitch black. I want a continuous light for focusing only, which switches off before the shutter opens.
Most modern flashes with PTTL will have an AF spotbeam, and most advanced flashes (i.e. anything except the Standard version of the Sigma flashes) will have a spotbeam only mode, meaning the AF beam will work but the flash will not fire.
Originally posted by timbo Not necessary, but desirable, would be a light which could adequately light say, an owl or roosting bird about 6-7 metres away while I focus, paired with a flash bulb that has adequate reach.
Any modern flash should work, though 6-7 meters might be nearing the limit of a spotbeam.